Policing and logging may be some of the highest-risk careers for prostate cancer, according to new research that also found a higher risk of aggressive tumours in bus and truck drivers — possibly because of the “whole body vibration” phenomenon.

The study, which involved nearly 2,000 men in Montreal’s French-speaking hospitals is one of the largest exploring possible links between occupation and the most frequently diagnosed cancer among Canadian men.

Studies dating back to the 1980s have shown farmers have a higher-than-normal risk of dying from this cancer.

However, other attempts have been “inconsistent or inconclusive,” and few job-based studies have taken into account the aggressiveness of the cancer when it was diagnosed, the team reports in the most recent issue of Environmental Health.

The new study involved 1,937 men aged 75 and younger newly diagnosed in 2005 -09, and a similar number of age-matched, healthy men randomly selected from electoral lists.

The men were interviewed in person and asked about every job they held for at least one year.

“We were focusing on each of the occupations they had held in the past — ‘What were your tasks? What were the chemicals you were using? Were you sitting? Walking?’ ” said principal investigator Marie-Elise Parent, of the Institut national de la recherche scientifique at the Université du Québec.

The analysis was conducted by doctoral student Jean-Francois Sauvé and Jérome Lavoué from the University of Montreal.

For the men with prostate cancer, the researchers also looked at their Gleason scores — the higher the number assigned to a tumour, the greater the risk of it spreading.

They found police officers, detectives and men working in forestry and logging were about twice as likely to have been diagnosed with prostate cancer as men never employed in those jobs.

Painters and decorators were three times more likely to develop prostate cancer. But there was also excess risk in several white-collar jobs, including public service, banking and finance — “jobs that typically entail few chemical exposures,” they noted, but tend to be sedentary desk jobs. Lack of physical activity in general, and obesity are thought to increase the risk.

Men who had worked as gas station attendants were more than four times as likely to be diagnosed with high-grade tumours, while bus drivers had triple the risk.

Ian Kucerak/Postmedia

The researchers are now trying to tease out “biologically plausible” explanations.

They previously published on a phenomenon known as occupational whole body vibration (WBV), whereby “mechanical energy is transmitted to the body” via vibrating surfaces, through the feet (if standing) or the trunk (if sitting).

Vibration has been linked with prostate abnormalities, such as prostatitis, inflammation of the prostate gland. Testosterone, another risk factor, also increases with WBV exposure, Parent said.

The phenomenon might also be at play for men in forestry and logging.

“We might wonder, could it be the vibration from the saws they are using,” Parent said. Alternatively, “Could it be the emissions from the engines, the diesel exhaust?”

For police, harmful exposures might include polycyclic aromatic hydrocarbons in exhausts, or non-ionizing radiation from radar guns, although the researchers acknowledge, “the intensity of exposure associated with the use of radar guns is generally very low.”

Could it be the vibration from the saws they are using?

Driving a bus and policing also can mean night and shift work, which can disrupt the body’s circadian rhythm and lead to lower levels of the sleep hormone melatonin, which helps regulate hormonal functions, including the hormones that regulate the prostate, Parent said.

Drivers also spend much of their day sitting and are exposed to diesel emissions containing known carcinogens. The fact they had more aggressive tumours suggests they may wait longer to get screened, Parent said.

The researchers are working with chemists and industrial hygienists to tease out which occupational “exposures and circumstances” may be important. The focus is on endocrine disruptors, hormone-altering chemicals in the environment that may promote or initiate cancer.

The findings surprised the Canadian Police Association.

“That certainly is interesting data, and (I) can confirm this is the first I’ve heard of it,” spokesman Michael Gendron said in an email. “We’ve seen studies that measure the impact of shift-work on first responders, but finding heightened instances of prostate cancer is new, at least as far as I know.

About 21,600 men will be diagnosed with prostate cancer this year, and 4,000 will die from the disease, according to the Canadian Cancer Society.